package model

import (
	"cmp"
	"hash/maphash"
	"iter"
	"slices"
	"strings"

	"github.com/ollama/ollama/x/types/structs"
)

const MaxNameLength = 255

type NamePart int

// Levels of concreteness
const (
	Invalid NamePart = iota
	Host
	Namespace
	Model
	Tag
	Build
)

var kindNames = map[NamePart]string{
	Invalid:   "Invalid",
	Host:      "Host",
	Namespace: "Namespace",
	Model:     "Name",
	Tag:       "Tag",
	Build:     "Build",
}

// Name is an opaque reference to a model.
//
// It is not comparable. To use as a map key, use [MapHash].
//
// Clients should use the [ParseName] function to create a Name from a string.
//
// The parts of a Name are:
//
//   - Host: the domain of the model (optional)
//   - Namespace: the namespace of the model (optional)
//   - Model: the name of the model (required)
//   - Tag: the tag of the model (optional)
//   - Build: the build of the model; usually the quantization or "file type" (optional)
//
// A call to [Name.Valid] will return true if the model has a valid non-empty model
// part.
//
// A call to [Name.Complete] will return true if the model has a valid model part
// and all of its other parts are also non-empty and valid.
type Name struct {
	_ structs.Incomparable

	host      string
	namespace string
	model     string
	tag       string
	build     string
}

var mapHashSeed = maphash.MakeSeed()

// MapHash returns a case insensitive hash for use in maps and equality
// checks. For a convienent way to compare names, use [Name.EqualFold].
func (r Name) MapHash() uint64 {
	// correctly hash the parts with case insensitive comparison
	var h maphash.Hash
	h.SetSeed(mapHashSeed)
	for _, part := range r.Parts() {
		// downcase the part for hashing
		for i := range part {
			c := part[i]
			if c >= 'A' && c <= 'Z' {
				c = c - 'A' + 'a'
			}
			h.WriteByte(c)
		}
	}
	return h.Sum64()
}

// Format returns a string representation of the ref with the given
// concreteness. If a part is missing, it is replaced with a loud
// placeholder.
func (r Name) Full() string {
	r.host = cmp.Or(r.host, "!(MISSING DOMAIN)")
	r.namespace = cmp.Or(r.namespace, "!(MISSING NAMESPACE)")
	r.model = cmp.Or(r.model, "!(MISSING NAME)")
	r.tag = cmp.Or(r.tag, "!(MISSING TAG)")
	r.build = cmp.Or(r.build, "!(MISSING BUILD)")
	return r.String()
}

func (r Name) ModelAndTag() string {
	r.host = ""
	r.namespace = ""
	r.build = ""
	return r.String()
}

func (r Name) ModelTagAndBuild() string {
	r.host = ""
	r.namespace = ""
	return r.String()
}

// String returns the fully qualified ref string.
func (r Name) String() string {
	var b strings.Builder
	if r.host != "" {
		b.WriteString(r.host)
		b.WriteString("/")
	}
	if r.namespace != "" {
		b.WriteString(r.namespace)
		b.WriteString("/")
	}
	b.WriteString(r.model)
	if r.tag != "" {
		b.WriteString(":")
		b.WriteString(r.tag)
	}
	if r.build != "" {
		b.WriteString("+")
		b.WriteString(r.build)
	}
	return b.String()
}

// Complete reports whether the ref is fully qualified. That is it has a
// domain, namespace, name, tag, and build.
func (r Name) Complete() bool {
	return r.Valid() && !slices.Contains(r.Parts(), "")
}

// CompleteWithoutBuild reports whether the ref would be complete if it had a
// valid build.
func (r Name) CompleteWithoutBuild() bool {
	r.build = "x"
	return r.Valid() && r.Complete()
}

// Less returns true if r is less concrete than o; false otherwise.
func (r Name) Less(o Name) bool {
	rp := r.Parts()
	op := o.Parts()
	for i := range rp {
		if rp[i] < op[i] {
			return true
		}
	}
	return false
}

// Parts returns the parts of the ref in order of concreteness.
//
// The length of the returned slice is always 5.
func (r Name) Parts() []string {
	return []string{
		r.host,
		r.namespace,
		r.model,
		r.tag,
		r.build,
	}
}

func (r Name) Host() string      { return r.host }
func (r Name) Namespace() string { return r.namespace }
func (r Name) Model() string     { return r.model }
func (r Name) Tag() string       { return r.tag }
func (r Name) Build() string     { return r.build }

// EqualFold reports whether r and o are equivalent model names, ignoring
// case.
func (r Name) EqualFold(o Name) bool {
	return r.MapHash() == o.MapHash()
}

// ParseName parses s into a Name. The input string must be a valid form of
// a model name in the form:
//
//	<host>/<namespace>/<model>:<tag>+<build>
//
// The name part is required, all others are optional. If a part is missing,
// it is left empty in the returned Name. If a part is invalid, the zero Ref
// value is returned.
//
// The build part is normalized to uppercase.
//
// Examples of valid paths:
//
//	"example.com/mistral:7b+x"
//	"example.com/mistral:7b+Q4_0"
//	"mistral:7b+x"
//	"example.com/x/mistral:latest+Q4_0"
//	"example.com/x/mistral:latest"
//
// Examples of invalid paths:
//
//	"example.com/mistral:7b+"
//	"example.com/mistral:7b+Q4_0+"
//	"x/y/z/z:8n+I"
//	""
func ParseName(s string) Name {
	var r Name
	for kind, part := range NameParts(s) {
		switch kind {
		case Host:
			r.host = part
		case Namespace:
			r.namespace = part
		case Model:
			r.model = part
		case Tag:
			r.tag = part
		case Build:
			r.build = strings.ToUpper(part)
		case Invalid:
			return Name{}
		}
	}
	if !r.Valid() {
		return Name{}
	}
	return r
}

// Merge performs a partial merge of src into dst. Only the non-name parts
// are merged. The name part is always left untouched. Other parts are
// merged if and only if they are missing in dst.
//
// Use this for merging a fully qualified ref with a partial ref, such as
// when filling in a missing parts with defaults.
//
// The returned Name will only be valid if dst is valid.
func Merge(dst, src Name) Name {
	return Name{
		// name is left untouched
		model: dst.model,

		host:      cmp.Or(dst.host, src.host),
		namespace: cmp.Or(dst.namespace, src.namespace),
		tag:       cmp.Or(dst.tag, src.tag),
		build:     cmp.Or(dst.build, src.build),
	}
}

// WithBuild returns a copy of r with the build set to the given string.
func (r Name) WithBuild(build string) Name {
	r.build = build
	return r
}

// Parts returns a sequence of the parts of a ref string from most specific
// to least specific.
//
// It normalizes the input string by removing "http://" and "https://" only.
// No other normalization is done.
//
// As a special case, question marks are ignored so they may be used as
// placeholders for missing parts in string literals.
func NameParts(s string) iter.Seq2[NamePart, string] {
	return func(yield func(NamePart, string) bool) {
		if strings.HasPrefix(s, "http://") {
			s = s[len("http://"):]
		}
		if strings.HasPrefix(s, "https://") {
			s = s[len("https://"):]
		}

		if len(s) > MaxNameLength || len(s) == 0 {
			return
		}

		yieldValid := func(kind NamePart, part string) bool {
			if !isValidPart(part) {
				yield(Invalid, "")
				return false
			}
			return yield(kind, part)
		}

		state, j := Build, len(s)
		for i := len(s) - 1; i >= 0; i-- {
			switch s[i] {
			case '+':
				switch state {
				case Build:
					if !yieldValid(Build, s[i+1:j]) {
						return
					}
					state, j = Tag, i
				default:
					yield(Invalid, "")
					return
				}
			case ':':
				switch state {
				case Build, Tag:
					if !yieldValid(Tag, s[i+1:j]) {
						return
					}
					state, j = Model, i
				default:
					yield(Invalid, "")
					return
				}
			case '/':
				switch state {
				case Model, Tag, Build:
					if !yieldValid(Model, s[i+1:j]) {
						return
					}
					state, j = Namespace, i
				case Namespace:
					if !yieldValid(Namespace, s[i+1:j]) {
						return
					}
					state, j = Host, i
				default:
					yield(Invalid, "")
					return
				}
			default:
				if !isValidPart(s[i : i+1]) {
					yield(Invalid, "")
					return
				}
			}
		}

		if state <= Namespace {
			yieldValid(state, s[:j])
		} else {
			yieldValid(Model, s[:j])
		}
	}
}

// Valid returns true if the ref has a valid nick. To know if a ref is
// "complete", use Complete.
func (r Name) Valid() bool {
	// Parts ensures we only have valid parts, so no need to validate
	// them here, only check if we have a name or not.
	return r.model != ""
}

// isValidPart returns true if given part is valid ascii [a-zA-Z0-9_\.-]
func isValidPart(s string) bool {
	if s == "" {
		return false
	}
	for _, c := range []byte(s) {
		if c == '.' || c == '-' {
			return true
		}
		if c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' || c == '_' {
			continue
		} else {
			return false

		}
	}
	return true
}