package commandmeta

import "strings"

// FlagTokenKind identifies the portion of the shared option grammar a token uses.
type FlagTokenKind uint8

const (
	OperandToken FlagTokenKind = iota
	TerminatorToken
	LongFlagToken
	ShortFlagToken
)

// ClassifyFlagToken distinguishes option tokens without consuming their values.
func ClassifyFlagToken(token string) FlagTokenKind {
	if token == "--" {
		return TerminatorToken
	}
	if strings.HasPrefix(token, "--") && len(token) > 2 {
		return LongFlagToken
	}
	if len(token) > 1 && token[0] == '-' {
		return ShortFlagToken
	}
	return OperandToken
}

// SplitLongFlag separates the entered spelling from an optional attached value.
func SplitLongFlag(token string) (spelling, value string, attached bool) {
	return strings.Cut(token, "=")
}

// FlagLookup maps canonical and applicable alias spellings to neutral flags.
type FlagLookup struct {
	canonical map[string]Flag
	aliases   map[string]Flag
}

// NewFlagLookup includes the built-in help flag alongside the supplied flags.
func NewFlagLookup(flags []Flag, aliases []FlagAlias) FlagLookup {
	canonical := make(map[string]Flag, len(flags)*2+2)
	help := HelpFlag()
	canonical["--help"], canonical["-h"] = help, help
	for _, flag := range flags {
		canonical["--"+flag.Name] = flag
		if flag.Short != "" {
			canonical["-"+flag.Short] = flag
		}
	}
	lookup := FlagLookup{canonical: canonical, aliases: make(map[string]Flag, len(aliases))}
	for _, alias := range aliases {
		if target, ok := canonical[alias.Target]; ok {
			lookup.aliases[alias.Source] = target
		}
	}
	return lookup
}

// Find returns the canonical flag for an entered spelling.
func (lookup FlagLookup) Find(spelling string) (Flag, bool) {
	flag, ok := lookup.canonical[spelling]
	if !ok {
		flag, ok = lookup.aliases[spelling]
	}
	return flag, ok
}

// FlagConsumption describes one flag within an option token. NextOffset is zero
// when the token is exhausted; otherwise it identifies the next short spelling.
type FlagConsumption struct {
	Flag       Flag
	Spelling   string
	Found      bool
	Value      string
	Attached   bool
	NeedsNext  bool
	NextOffset int
}

// ConsumeFlag reads a long option or a short option at offset in a cluster.
func ConsumeFlag(lookup FlagLookup, token string, offset int) FlagConsumption {
	var result FlagConsumption
	if ClassifyFlagToken(token) == LongFlagToken {
		result.Spelling, result.Value, result.Attached = SplitLongFlag(token)
		result.Flag, result.Found = lookup.Find(result.Spelling)
		result.NeedsNext = result.Found && !result.Flag.Boolean && !result.Attached
		return result
	}
	result.Spelling = "-" + token[offset:offset+1]
	result.Flag, result.Found = lookup.Find(result.Spelling)
	if !result.Found {
		return result
	}
	suffix := token[offset+1:]
	if result.Flag.Boolean {
		if strings.HasPrefix(suffix, "=") {
			result.Attached, result.Value = true, suffix[1:]
		} else if suffix != "" {
			result.NextOffset = offset + 1
		}
		return result
	}
	if suffix == "" {
		result.NeedsNext = true
		return result
	}
	result.Attached = true
	result.Value = strings.TrimPrefix(suffix, "=")
	return result
}