package logger

// Logging is currently designed to look and feel like clang's error format.
// Errors are streamed asynchronously as they happen, each error contains the
// contents of the line with the error, and the error count is limited by
// default.

import (
	"fmt"
	"os"
	"runtime"
	"sort"
	"strings"
	"sync"
	"time"
	"unicode/utf8"
)

const defaultTerminalWidth = 80

type Log struct {
	AddMsg    func(Msg)
	HasErrors func() bool
	Done      func() []Msg
}

type LogLevel int8

const (
	LevelNone LogLevel = iota
	LevelInfo
	LevelWarning
	LevelError
	LevelSilent
)

type MsgKind uint8

const (
	Error MsgKind = iota
	Warning
	Note
)

func (kind MsgKind) String() string {
	switch kind {
	case Error:
		return "error"
	case Warning:
		return "warning"
	case Note:
		return "note"
	default:
		panic("Internal error")
	}
}

type Msg struct {
	Kind  MsgKind
	Data  MsgData
	Notes []MsgData
}

type MsgData struct {
	Text     string
	Location *MsgLocation

	// Optional user-specified data that is passed through unmodified
	UserDetail interface{}
}

type MsgLocation struct {
	File       string
	Namespace  string
	Line       int // 1-based
	Column     int // 0-based, in bytes
	Length     int // in bytes
	LineText   string
	Suggestion string
}

type Loc struct {
	// This is the 0-based index of this location from the start of the file, in bytes
	Start int32
}

type Range struct {
	Loc Loc
	Len int32
}

func (r Range) End() int32 {
	return r.Loc.Start + r.Len
}

// This type is just so we can use Go's native sort function
type SortableMsgs []Msg

func (a SortableMsgs) Len() int          { return len(a) }
func (a SortableMsgs) Swap(i int, j int) { a[i], a[j] = a[j], a[i] }

func (a SortableMsgs) Less(i int, j int) bool {
	ai := a[i]
	aj := a[j]
	aiLoc := ai.Data.Location
	ajLoc := aj.Data.Location
	if aiLoc == nil || ajLoc == nil {
		return aiLoc == nil && ajLoc != nil
	}
	if aiLoc.File != ajLoc.File {
		return aiLoc.File < ajLoc.File
	}
	if aiLoc.Line != ajLoc.Line {
		return aiLoc.Line < ajLoc.Line
	}
	if aiLoc.Column != ajLoc.Column {
		return aiLoc.Column < ajLoc.Column
	}
	if ai.Kind != aj.Kind {
		return ai.Kind < aj.Kind
	}
	return ai.Data.Text < aj.Data.Text
}

// This is used to represent both file system paths (Namespace == "file") and
// abstract module paths (Namespace != "file"). Abstract module paths represent
// "virtual modules" when used for an input file and "package paths" when used
// to represent an external module.
type Path struct {
	Text      string
	Namespace string
	Flags     PathFlags
}

type PathFlags uint8

const (
	// This corresponds to a value of "false' in the "browser" package.json field
	PathDisabled PathFlags = 1 << iota
)

func (p Path) IsDisabled() bool {
	return (p.Flags & PathDisabled) != 0
}

func (a Path) ComesBeforeInSortedOrder(b Path) bool {
	return a.Namespace > b.Namespace ||
		(a.Namespace == b.Namespace && (a.Text < b.Text ||
			(a.Text == b.Text && a.Flags < b.Flags)))
}

// This has a custom implementation instead of using "filepath.Dir/Base/Ext"
// because it should work the same on Unix and Windows. These names end up in
// the generated output and the generated output should not depend on the OS.
func PlatformIndependentPathDirBaseExt(path string) (dir string, base string, ext string) {
	for {
		i := strings.LastIndexAny(path, "/\\")

		// Stop if there are no more slashes
		if i < 0 {
			base = path
			break
		}

		// Stop if we found a non-trailing slash
		if i+1 != len(path) {
			dir, base = path[:i], path[i+1:]
			break
		}

		// Ignore trailing slashes
		path = path[:i]
	}

	// Strip off the extension
	if dot := strings.LastIndexByte(base, '.'); dot >= 0 {
		base, ext = base[:dot], base[dot:]
	}

	return
}

type Source struct {
	Index uint32

	// This is used as a unique key to identify this source file. It should never
	// be shown to the user (e.g. never print this to the terminal).
	//
	// If it's marked as an absolute path, it's a platform-dependent path that
	// includes environment-specific things such as Windows backslash path
	// separators and potentially the user's home directory. Only use this for
	// passing to syscalls for reading and writing to the file system. Do not
	// include this in any output data.
	//
	// If it's marked as not an absolute path, it's an opaque string that is used
	// to refer to an automatically-generated module.
	KeyPath Path

	// This is used for error messages and the metadata JSON file.
	//
	// This is a mostly platform-independent path. It's relative to the current
	// working directory and always uses standard path separators. Use this for
	// referencing a file in all output data. These paths still use the original
	// case of the path so they may still work differently on file systems that
	// are case-insensitive vs. case-sensitive.
	PrettyPath string

	// An identifier that is mixed in to automatically-generated symbol names to
	// improve readability. For example, if the identifier is "util" then the
	// symbol for an "export default" statement will be called "util_default".
	IdentifierName string

	Contents string
}

func (s *Source) TextForRange(r Range) string {
	return s.Contents[r.Loc.Start : r.Loc.Start+r.Len]
}

func (s *Source) RangeOfOperatorBefore(loc Loc, op string) Range {
	text := s.Contents[:loc.Start]
	index := strings.LastIndex(text, op)
	if index >= 0 {
		return Range{Loc: Loc{Start: int32(index)}, Len: int32(len(op))}
	}
	return Range{Loc: loc}
}

func (s *Source) RangeOfOperatorAfter(loc Loc, op string) Range {
	text := s.Contents[loc.Start:]
	index := strings.Index(text, op)
	if index >= 0 {
		return Range{Loc: Loc{Start: loc.Start + int32(index)}, Len: int32(len(op))}
	}
	return Range{Loc: loc}
}

func (s *Source) RangeOfString(loc Loc) Range {
	text := s.Contents[loc.Start:]
	if len(text) == 0 {
		return Range{Loc: loc, Len: 0}
	}

	quote := text[0]
	if quote == '"' || quote == '\'' {
		// Search for the matching quote character
		for i := 1; i < len(text); i++ {
			c := text[i]
			if c == quote {
				return Range{Loc: loc, Len: int32(i + 1)}
			} else if c == '\\' {
				i += 1
			}
		}
	}

	return Range{Loc: loc, Len: 0}
}

func (s *Source) RangeOfNumber(loc Loc) (r Range) {
	text := s.Contents[loc.Start:]
	r = Range{Loc: loc, Len: 0}

	if len(text) > 0 {
		if c := text[0]; c >= '0' && c <= '9' {
			r.Len = 1
			for int(r.Len) < len(text) {
				c := text[r.Len]
				if (c < '0' || c > '9') && (c < 'a' || c > 'z') && (c < 'A' || c > 'Z') && c != '.' && c != '_' {
					break
				}
				r.Len++
			}
		}
	}
	return
}

func plural(prefix string, count int) string {
	if count == 1 {
		return fmt.Sprintf("%d %s", count, prefix)
	}
	return fmt.Sprintf("%d %ss", count, prefix)
}

func errorAndWarningSummary(errors int, warnings int) string {
	switch {
	case errors == 0:
		return plural("warning", warnings)
	case warnings == 0:
		return plural("error", errors)
	default:
		return fmt.Sprintf("%s and %s",
			plural("warning", warnings),
			plural("error", errors))
	}
}

type TerminalInfo struct {
	IsTTY           bool
	UseColorEscapes bool
	Width           int
}

func NewStderrLog(options OutputOptions) Log {
	var mutex sync.Mutex
	var msgs SortableMsgs
	terminalInfo := GetTerminalInfo(os.Stderr)
	errors := 0
	warnings := 0
	errorLimitWasHit := false

	switch options.Color {
	case ColorNever:
		terminalInfo.UseColorEscapes = false
	case ColorAlways:
		terminalInfo.UseColorEscapes = SupportsColorEscapes
	}

	return Log{
		AddMsg: func(msg Msg) {
			mutex.Lock()
			defer mutex.Unlock()
			msgs = append(msgs, msg)

			// Be silent if we're past the limit so we don't flood the terminal
			if errorLimitWasHit {
				return
			}

			switch msg.Kind {
			case Error:
				errors++
				if options.LogLevel <= LevelError {
					writeStringWithColor(os.Stderr, msg.String(options, terminalInfo))
				}
			case Warning:
				warnings++
				if options.LogLevel <= LevelWarning {
					writeStringWithColor(os.Stderr, msg.String(options, terminalInfo))
				}
			}

			// Silence further output if we reached the error limit
			if options.ErrorLimit != 0 && errors >= options.ErrorLimit {
				errorLimitWasHit = true
				if options.LogLevel <= LevelError {
					writeStringWithColor(os.Stderr, fmt.Sprintf(
						"%s reached (disable error limit with --error-limit=0)\n", errorAndWarningSummary(errors, warnings)))
				}
			}
		},
		HasErrors: func() bool {
			mutex.Lock()
			defer mutex.Unlock()
			return errors > 0
		},
		Done: func() []Msg {
			mutex.Lock()
			defer mutex.Unlock()

			// Print out a summary if the error limit wasn't hit
			if !errorLimitWasHit && options.LogLevel <= LevelInfo && (warnings != 0 || errors != 0) {
				writeStringWithColor(os.Stderr, fmt.Sprintf("%s\n", errorAndWarningSummary(errors, warnings)))
			}

			sort.Stable(msgs)
			return msgs
		},
	}
}

func PrintErrorToStderr(osArgs []string, text string) {
	PrintMessageToStderr(osArgs, Msg{Kind: Error, Data: MsgData{Text: text}})
}

func OutputOptionsForArgs(osArgs []string) OutputOptions {
	options := OutputOptions{IncludeSource: true}

	// Implement a mini argument parser so these options always work even if we
	// haven't yet gotten to the general-purpose argument parsing code
	for _, arg := range osArgs {
		switch arg {
		case "--color=false":
			options.Color = ColorNever
		case "--color=true":
			options.Color = ColorAlways
		case "--log-level=info":
			options.LogLevel = LevelInfo
		case "--log-level=warning":
			options.LogLevel = LevelWarning
		case "--log-level=error":
			options.LogLevel = LevelError
		case "--log-level=silent":
			options.LogLevel = LevelSilent
		}
	}

	return options
}

func PrintMessageToStderr(osArgs []string, msg Msg) {
	log := NewStderrLog(OutputOptionsForArgs(osArgs))
	log.AddMsg(msg)
	log.Done()
}

type Colors struct {
	Default string
	Bold    string
	Dim     string

	Red   string
	Green string
	Blue  string

	Cyan    string
	Magenta string
	Yellow  string

	Underline string
}

func PrintText(file *os.File, level LogLevel, osArgs []string, callback func(Colors) string) {
	options := OutputOptionsForArgs(osArgs)

	// Skip logging these if these logs are disabled
	if options.LogLevel > level {
		return
	}

	PrintTextWithColor(file, options.Color, callback)
}

func PrintTextWithColor(file *os.File, useColor UseColor, callback func(Colors) string) {
	var useColorEscapes bool
	switch useColor {
	case ColorNever:
		useColorEscapes = false
	case ColorAlways:
		useColorEscapes = SupportsColorEscapes
	case ColorIfTerminal:
		useColorEscapes = GetTerminalInfo(file).UseColorEscapes
	}

	var colors Colors
	if useColorEscapes {
		colors.Default = colorReset
		colors.Bold = colorResetBold
		colors.Dim = colorResetDim

		colors.Red = colorRed
		colors.Green = colorGreen
		colors.Blue = colorBlue

		colors.Cyan = colorCyan
		colors.Magenta = colorMagenta
		colors.Yellow = colorYellow

		colors.Underline = colorResetUnderline
	}
	writeStringWithColor(file, callback(colors))
}

type SummaryTableEntry struct {
	Dir         string
	Base        string
	Size        string
	Bytes       int
	IsSourceMap bool
}

// This type is just so we can use Go's native sort function
type SummaryTable []SummaryTableEntry

func (t SummaryTable) Len() int          { return len(t) }
func (t SummaryTable) Swap(i int, j int) { t[i], t[j] = t[j], t[i] }

func (t SummaryTable) Less(i int, j int) bool {
	ti := t[i]
	tj := t[j]

	// Sort source maps last
	if !ti.IsSourceMap && tj.IsSourceMap {
		return true
	}
	if ti.IsSourceMap && !tj.IsSourceMap {
		return false
	}

	// Sort by size first
	if ti.Bytes > tj.Bytes {
		return true
	}
	if ti.Bytes < tj.Bytes {
		return false
	}

	// Sort subdirectories first
	if strings.HasPrefix(ti.Dir, tj.Dir) {
		return true
	}
	if strings.HasPrefix(tj.Dir, ti.Dir) {
		return false
	}

	// Sort alphabetically by directory first
	if ti.Dir < tj.Dir {
		return true
	}
	if ti.Dir > tj.Dir {
		return false
	}

	// Then sort alphabetically by file name
	return ti.Base < tj.Base
}

// Show a warning icon next to output files that are 1mb or larger
const sizeWarningThreshold = 1024 * 1024

func PrintSummary(osArgs []string, table SummaryTable, start time.Time) {
	PrintText(os.Stderr, LevelInfo, osArgs, func(colors Colors) string {
		isProbablyWindowsCommandPrompt := false
		sb := strings.Builder{}

		// Assume we are running in Windows Command Prompt if we're on Windows. If
		// so, we can't use emoji because it won't be supported. Except we can
		// still use emoji if the WT_SESSION environment variable is present
		// because that means we're running in the new Windows Terminal instead.
		if runtime.GOOS == "windows" {
			isProbablyWindowsCommandPrompt = true
			for _, env := range os.Environ() {
				if strings.HasPrefix(env, "WT_SESSION=") {
					isProbablyWindowsCommandPrompt = false
					break
				}
			}
		}

		if len(table) > 0 {
			// Compute the maximum width of the size column
			spacingBetweenColumns := 2
			hasSizeWarning := false
			maxPath := 0
			maxSize := 0
			for _, entry := range table {
				path := len(entry.Dir) + len(entry.Base)
				size := len(entry.Size) + spacingBetweenColumns
				if path > maxPath {
					maxPath = path
				}
				if size > maxSize {
					maxSize = size
				}
				if !entry.IsSourceMap && entry.Bytes >= sizeWarningThreshold {
					hasSizeWarning = true
				}
			}

			margin := "  "
			layoutWidth := GetTerminalInfo(os.Stderr).Width
			if layoutWidth < 1 {
				layoutWidth = defaultTerminalWidth
			}
			layoutWidth -= 2 * len(margin)
			if hasSizeWarning {
				// Add space for the warning icon
				layoutWidth -= 2
			}
			if layoutWidth > maxPath+maxSize {
				layoutWidth = maxPath + maxSize
			}
			sort.Sort(table)
			sb.WriteString("\n")

			wasSourceMap := false
			for i, entry := range table {
				dir, base := entry.Dir, entry.Base
				pathWidth := layoutWidth - maxSize

				// Truncate the path with "..." to fit on one line
				if len(dir)+len(base) > pathWidth {
					// Trim the directory from the front, leaving the trailing slash
					if len(dir) > 0 {
						n := pathWidth - len(base) - 3
						if n < 1 {
							n = 1
						}
						dir = "..." + dir[len(dir)-n:]
					}

					// Trim the file name from the back
					if len(dir)+len(base) > pathWidth {
						n := pathWidth - len(dir) - 3
						if n < 0 {
							n = 0
						}
						base = base[:n] + "..."
					}
				}

				spacer := layoutWidth - len(entry.Size) - len(dir) - len(base)
				if spacer < 0 {
					spacer = 0
				}

				// Print a boundary in between normal files and source map files if
				// there was more than one normal file. This improves scannability.
				if !wasSourceMap && entry.IsSourceMap && i > 1 {
					sb.WriteString("\n")
					wasSourceMap = true
				}

				// Put a warning next to the size if it's above a certain threshold
				sizeColor := colors.Cyan
				sizeWarning := ""
				if !entry.IsSourceMap && entry.Bytes >= sizeWarningThreshold {
					sizeColor = colors.Yellow

					// Emoji don't work in Windows Command Prompt
					if !isProbablyWindowsCommandPrompt {
						sizeWarning = " ⚠️"
					}
				}

				sb.WriteString(fmt.Sprintf("%s%s%s%s%s%s%s%s%s%s%s\n",
					margin,
					colors.Dim,
					dir,
					colors.Bold,
					base,
					colors.Default,
					strings.Repeat(" ", spacer),
					sizeColor,
					entry.Size,
					sizeWarning,
					colors.Default,
				))
			}
		}

		lightningSymbol := "⚡ "

		// Emoji don't work in Windows Command Prompt
		if isProbablyWindowsCommandPrompt {
			lightningSymbol = ""
		}

		sb.WriteString(fmt.Sprintf("\n%s%sDone in %dms%s\n\n",
			lightningSymbol,
			colors.Green,
			time.Since(start).Milliseconds(),
			colors.Default,
		))
		return sb.String()
	})
}

func NewDeferLog() Log {
	var msgs SortableMsgs
	var mutex sync.Mutex
	var hasErrors bool

	return Log{
		AddMsg: func(msg Msg) {
			mutex.Lock()
			defer mutex.Unlock()
			if msg.Kind == Error {
				hasErrors = true
			}
			msgs = append(msgs, msg)
		},
		HasErrors: func() bool {
			mutex.Lock()
			defer mutex.Unlock()
			return hasErrors
		},
		Done: func() []Msg {
			mutex.Lock()
			defer mutex.Unlock()
			sort.Stable(msgs)
			return msgs
		},
	}
}

const colorReset = "\033[0m"

const colorRed = "\033[31m"
const colorGreen = "\033[32m"
const colorBlue = "\033[34m"

const colorCyan = "\033[36m"
const colorMagenta = "\033[35m"
const colorYellow = "\033[33m"

const colorResetDim = "\033[0;37m"
const colorBold = "\033[1m"
const colorResetBold = "\033[0;1m"
const colorResetUnderline = "\033[0;4m"

type UseColor uint8

const (
	ColorIfTerminal UseColor = iota
	ColorNever
	ColorAlways
)

type OutputOptions struct {
	IncludeSource bool
	ErrorLimit    int
	Color         UseColor
	LogLevel      LogLevel
}

func (msg Msg) String(options OutputOptions, terminalInfo TerminalInfo) string {
	// Compute the maximum margin
	maxMargin := 0
	if options.IncludeSource {
		if msg.Data.Location != nil {
			maxMargin = len(fmt.Sprintf("%d", msg.Data.Location.Line))
		}
		for _, note := range msg.Notes {
			if note.Location != nil {
				margin := len(fmt.Sprintf("%d", note.Location.Line))
				if margin > maxMargin {
					maxMargin = margin
				}
			}
		}
	}

	// Format the message
	text := msgString(options, terminalInfo, msg.Kind, msg.Data, maxMargin)

	// Put a blank line between the message and the notes if the message has a stack trace
	gap := ""
	if loc := msg.Data.Location; loc != nil && strings.ContainsRune(loc.LineText, '\n') {
		gap = "\n"
	}

	// Format the notes
	for _, note := range msg.Notes {
		text += gap
		text += msgString(options, terminalInfo, Note, note, maxMargin)
	}

	// Add extra spacing between messages if source code is present
	if options.IncludeSource {
		text += "\n"
	}
	return text
}

// The number of margin characters in addition to the line number
const extraMarginChars = 7

func marginWithLineText(maxMargin int, line int) string {
	number := fmt.Sprintf("%d", line)
	return fmt.Sprintf("    %s%s │ ", strings.Repeat(" ", maxMargin-len(number)), number)
}

func emptyMarginText(maxMargin int, isLast bool) string {
	space := strings.Repeat(" ", maxMargin)
	if isLast {
		return fmt.Sprintf("    %s ╵ ", space)
	}
	return fmt.Sprintf("    %s │ ", space)
}

func msgString(options OutputOptions, terminalInfo TerminalInfo, kind MsgKind, data MsgData, maxMargin int) string {
	var kindColor string
	textColor := colorBold
	textResetColor := colorResetBold
	textIndent := ""

	if options.IncludeSource {
		textIndent = " > "
	}

	switch kind {
	case Error:
		kindColor = colorRed

	case Warning:
		kindColor = colorMagenta

	case Note:
		textColor = colorReset
		kindColor = colorResetBold
		textResetColor = colorReset
		if options.IncludeSource {
			textIndent = "   "
		}

	default:
		panic("Internal error")
	}

	if data.Location == nil {
		if terminalInfo.UseColorEscapes {
			return fmt.Sprintf("%s%s%s%s: %s%s%s\n",
				textColor, textIndent, kindColor, kind.String(),
				textResetColor, data.Text,
				colorReset)
		}

		return fmt.Sprintf("%s%s: %s\n", textIndent, kind.String(), data.Text)
	}

	if !options.IncludeSource {
		if terminalInfo.UseColorEscapes {
			return fmt.Sprintf("%s%s%s: %s%s: %s%s%s\n",
				textColor, textIndent, data.Location.File,
				kindColor, kind.String(),
				textResetColor, data.Text,
				colorReset)
		}

		return fmt.Sprintf("%s%s: %s: %s\n",
			textIndent, data.Location.File, kind.String(), data.Text)
	}

	d := detailStruct(data, terminalInfo, maxMargin)

	if terminalInfo.UseColorEscapes {
		if d.Suggestion != "" {
			return fmt.Sprintf("%s%s%s: %s%s: %s%s\n%s%s%s%s%s%s\n%s%s%s%s%s\n%s%s%s%s%s%s%s\n",
				textColor, textIndent, d.Path,
				kindColor, kind.String(),
				textResetColor, d.Message,
				colorResetDim, d.SourceBefore, colorGreen, d.SourceMarked, colorResetDim, d.SourceAfter,
				emptyMarginText(maxMargin, false), d.Indent, colorGreen, d.Marker, colorResetDim,
				emptyMarginText(maxMargin, true), d.Indent, colorGreen, d.Suggestion, colorResetDim,
				d.ContentAfter, colorReset)
		}

		return fmt.Sprintf("%s%s%s: %s%s: %s%s\n%s%s%s%s%s%s\n%s%s%s%s%s%s%s\n",
			textColor, textIndent, d.Path,
			kindColor, kind.String(),
			textResetColor, d.Message,
			colorResetDim, d.SourceBefore, colorGreen, d.SourceMarked, colorResetDim, d.SourceAfter,
			emptyMarginText(maxMargin, true), d.Indent, colorGreen, d.Marker, colorResetDim,
			d.ContentAfter, colorReset)
	}

	if d.Suggestion != "" {
		return fmt.Sprintf("%s%s: %s: %s\n%s%s%s\n%s%s%s\n%s%s%s%s\n",
			textIndent, d.Path, kind.String(), d.Message,
			d.SourceBefore, d.SourceMarked, d.SourceAfter,
			emptyMarginText(maxMargin, false), d.Indent, d.Marker,
			emptyMarginText(maxMargin, true), d.Indent, d.Suggestion,
			d.ContentAfter)
	}

	return fmt.Sprintf("%s%s: %s: %s\n%s%s%s\n%s%s%s%s\n",
		textIndent, d.Path, kind.String(), d.Message,
		d.SourceBefore, d.SourceMarked, d.SourceAfter,
		emptyMarginText(maxMargin, true), d.Indent, d.Marker,
		d.ContentAfter)
}

type MsgDetail struct {
	Path    string
	Line    int
	Column  int
	Message string

	SourceBefore string
	SourceMarked string
	SourceAfter  string

	Indent     string
	Marker     string
	Suggestion string

	ContentAfter string
}

func computeLineAndColumn(contents string, offset int) (lineCount int, columnCount int, lineStart int, lineEnd int) {
	var prevCodePoint rune
	if offset > len(contents) {
		offset = len(contents)
	}

	// Scan up to the offset and count lines
	for i, codePoint := range contents[:offset] {
		switch codePoint {
		case '\n':
			lineStart = i + 1
			if prevCodePoint != '\r' {
				lineCount++
			}
		case '\r':
			lineStart = i + 1
			lineCount++
		case '\u2028', '\u2029':
			lineStart = i + 3 // These take three bytes to encode in UTF-8
			lineCount++
		}
		prevCodePoint = codePoint
	}

	// Scan to the end of the line (or end of file if this is the last line)
	lineEnd = len(contents)
loop:
	for i, codePoint := range contents[offset:] {
		switch codePoint {
		case '\r', '\n', '\u2028', '\u2029':
			lineEnd = offset + i
			break loop
		}
	}

	columnCount = offset - lineStart
	return
}

func LocationOrNil(source *Source, r Range) *MsgLocation {
	if source == nil {
		return nil
	}

	// Convert the index into a line and column number
	lineCount, columnCount, lineStart, lineEnd := computeLineAndColumn(source.Contents, int(r.Loc.Start))

	return &MsgLocation{
		File:     source.PrettyPath,
		Line:     lineCount + 1, // 0-based to 1-based
		Column:   columnCount,
		Length:   int(r.Len),
		LineText: source.Contents[lineStart:lineEnd],
	}
}

func detailStruct(data MsgData, terminalInfo TerminalInfo, maxMargin int) MsgDetail {
	// Only highlight the first line of the line text
	loc := *data.Location
	endOfFirstLine := len(loc.LineText)
	for i, c := range loc.LineText {
		if c == '\r' || c == '\n' || c == '\u2028' || c == '\u2029' {
			endOfFirstLine = i
			break
		}
	}
	firstLine := loc.LineText[:endOfFirstLine]
	afterFirstLine := loc.LineText[endOfFirstLine:]

	// Clamp values in range
	if loc.Line < 0 {
		loc.Line = 0
	}
	if loc.Column < 0 {
		loc.Column = 0
	}
	if loc.Length < 0 {
		loc.Length = 0
	}
	if loc.Column > endOfFirstLine {
		loc.Column = endOfFirstLine
	}
	if loc.Length > endOfFirstLine-loc.Column {
		loc.Length = endOfFirstLine - loc.Column
	}

	spacesPerTab := 2
	lineText := renderTabStops(firstLine, spacesPerTab)
	textUpToLoc := renderTabStops(firstLine[:loc.Column], spacesPerTab)
	markerStart := len(textUpToLoc)
	markerEnd := markerStart
	indent := strings.Repeat(" ", estimateWidthInTerminal(textUpToLoc))
	marker := "^"

	// Extend markers to cover the full range of the error
	if loc.Length > 0 {
		markerEnd = len(renderTabStops(firstLine[:loc.Column+loc.Length], spacesPerTab))
	}

	// Clip the marker to the bounds of the line
	if markerStart > len(lineText) {
		markerStart = len(lineText)
	}
	if markerEnd > len(lineText) {
		markerEnd = len(lineText)
	}
	if markerEnd < markerStart {
		markerEnd = markerStart
	}

	// Trim the line to fit the terminal width
	width := terminalInfo.Width
	if width < 1 {
		width = defaultTerminalWidth
	}
	width -= maxMargin + extraMarginChars
	if width < 1 {
		width = 1
	}
	if loc.Column == endOfFirstLine {
		// If the marker is at the very end of the line, the marker will be a "^"
		// character that extends one column past the end of the line. In this case
		// we should reserve a column at the end so the marker doesn't wrap.
		width -= 1
	}
	if len(lineText) > width {
		// Try to center the error
		sliceStart := (markerStart + markerEnd - width) / 2
		if sliceStart > markerStart-width/5 {
			sliceStart = markerStart - width/5
		}
		if sliceStart < 0 {
			sliceStart = 0
		}
		if sliceStart > len(lineText)-width {
			sliceStart = len(lineText) - width
		}
		sliceEnd := sliceStart + width

		// Slice the line
		slicedLine := lineText[sliceStart:sliceEnd]
		markerStart -= sliceStart
		markerEnd -= sliceStart
		if markerStart < 0 {
			markerStart = 0
		}
		if markerEnd > len(slicedLine) {
			markerEnd = len(slicedLine)
		}

		// Truncate the ends with "..."
		if len(slicedLine) > 3 && sliceStart > 0 {
			slicedLine = "..." + slicedLine[3:]
			if markerStart < 3 {
				markerStart = 3
			}
		}
		if len(slicedLine) > 3 && sliceEnd < len(lineText) {
			slicedLine = slicedLine[:len(slicedLine)-3] + "..."
			if markerEnd > len(slicedLine)-3 {
				markerEnd = len(slicedLine) - 3
			}
			if markerEnd < markerStart {
				markerEnd = markerStart
			}
		}

		// Now we can compute the indent
		lineText = slicedLine
		indent = strings.Repeat(" ", estimateWidthInTerminal(lineText[:markerStart]))
	}

	// If marker is still multi-character after clipping, make the marker wider
	if markerEnd-markerStart > 1 {
		marker = strings.Repeat("~", estimateWidthInTerminal(lineText[markerStart:markerEnd]))
	}

	// Put a margin before the marker indent
	margin := marginWithLineText(maxMargin, loc.Line)

	return MsgDetail{
		Path:    loc.File,
		Line:    loc.Line,
		Column:  loc.Column,
		Message: data.Text,

		SourceBefore: margin + lineText[:markerStart],
		SourceMarked: lineText[markerStart:markerEnd],
		SourceAfter:  lineText[markerEnd:],

		Indent:     indent,
		Marker:     marker,
		Suggestion: loc.Suggestion,

		ContentAfter: afterFirstLine,
	}
}

// Estimate the number of columns this string will take when printed
func estimateWidthInTerminal(text string) int {
	// For now just assume each code point is one column. This is wrong but is
	// less wrong than assuming each code unit is one column.
	width := 0
	for text != "" {
		_, size := utf8.DecodeRuneInString(text)
		text = text[size:]
		width++
	}
	return width
}

func renderTabStops(withTabs string, spacesPerTab int) string {
	if !strings.ContainsRune(withTabs, '\t') {
		return withTabs
	}

	withoutTabs := strings.Builder{}
	count := 0

	for _, c := range withTabs {
		if c == '\t' {
			spaces := spacesPerTab - count%spacesPerTab
			for i := 0; i < spaces; i++ {
				withoutTabs.WriteRune(' ')
				count++
			}
		} else {
			withoutTabs.WriteRune(c)
			count++
		}
	}

	return withoutTabs.String()
}

func (log Log) AddError(source *Source, loc Loc, text string) {
	log.AddMsg(Msg{
		Kind: Error,
		Data: RangeData(source, Range{Loc: loc}, text),
	})
}

func (log Log) AddErrorWithNotes(source *Source, loc Loc, text string, notes []MsgData) {
	log.AddMsg(Msg{
		Kind:  Error,
		Data:  RangeData(source, Range{Loc: loc}, text),
		Notes: notes,
	})
}

func (log Log) AddWarning(source *Source, loc Loc, text string) {
	log.AddMsg(Msg{
		Kind: Warning,
		Data: RangeData(source, Range{Loc: loc}, text),
	})
}

func (log Log) AddRangeError(source *Source, r Range, text string) {
	log.AddMsg(Msg{
		Kind: Error,
		Data: RangeData(source, r, text),
	})
}

func (log Log) AddRangeWarning(source *Source, r Range, text string) {
	log.AddMsg(Msg{
		Kind: Warning,
		Data: RangeData(source, r, text),
	})
}

func (log Log) AddRangeErrorWithNotes(source *Source, r Range, text string, notes []MsgData) {
	log.AddMsg(Msg{
		Kind:  Error,
		Data:  RangeData(source, r, text),
		Notes: notes,
	})
}

func (log Log) AddRangeWarningWithNotes(source *Source, r Range, text string, notes []MsgData) {
	log.AddMsg(Msg{
		Kind:  Warning,
		Data:  RangeData(source, r, text),
		Notes: notes,
	})
}

func RangeData(source *Source, r Range, text string) MsgData {
	return MsgData{
		Text:     text,
		Location: LocationOrNil(source, r),
	}
}