package execenv

import (
	"fmt"
	"strconv"
	"strings"
)

// Wheel 是索引里的一个候选。Kind 为 wheel 或 sdist。
type Wheel struct {
	Name     string
	Version  string
	Filename string
	SHA256   string
	Kind     string
	Requires []string
	Size     int64
}

// Result 是一次解析。Packages 只含相对约束新增的包，不含基础层已有的。
type Result struct {
	Packages []LockedPkg
	Override []string
	SDist    []string
	Missing  []string
	Denied   []string
}

func (r Result) OK() bool {
	return len(r.Override) == 0 && len(r.SDist) == 0 && len(r.Missing) == 0 && len(r.Denied) == 0
}

// ResolveMem 用内存索引解析。基础层里已有且版本满足的包不会进入 Packages。
// 版本不满足时记入 Override，不改约束。
func ResolveMem(index []Wheel, reqs []string, constraints []LockedPkg) Result {
	byName := map[string][]Wheel{}
	for _, w := range index {
		byName[normName(w.Name)] = append(byName[normName(w.Name)], w)
	}
	pinned := map[string]LockedPkg{}
	for _, c := range constraints {
		pinned[normName(c.Name)] = c
	}
	chosen := map[string]LockedPkg{}
	var res Result
	queue := append([]string{}, reqs...)
	seen := map[string]bool{}
	for len(queue) > 0 {
		req := strings.TrimSpace(queue[0])
		queue = queue[1:]
		if req == "" {
			continue
		}
		name, spec := splitReq(req)
		key := normName(name)
		mark := key + "\x00" + spec
		if seen[mark] {
			continue
		}
		seen[mark] = true
		if pin, ok := pinned[key]; ok {
			if spec != "" && !matchSpec(pin.Version, spec) {
				res.Override = append(res.Override, fmt.Sprintf("%s 需要 %s，基础层固定为 %s", name, spec, pin.Version))
			}
			continue
		}
		if prev, ok := chosen[key]; ok {
			if spec != "" && !matchSpec(prev.Version, spec) {
				res.Override = append(res.Override, fmt.Sprintf("%s 需要 %s，已选 %s", name, spec, prev.Version))
			}
			continue
		}
		best, sdist := pickWheel(byName[key], spec)
		if sdist && best == nil {
			res.SDist = append(res.SDist, name)
			continue
		}
		if best == nil {
			res.Missing = append(res.Missing, name)
			continue
		}
		pkg := LockedPkg{
			Name: best.Name, Version: best.Version, Filename: best.Filename,
			SHA256: best.SHA256, Size: best.Size,
		}
		chosen[key] = pkg
		for _, dep := range best.Requires {
			queue = append(queue, dep)
		}
	}
	names := make([]string, 0, len(chosen))
	for n := range chosen {
		names = append(names, n)
	}
	sortStrings(names)
	for _, n := range names {
		res.Packages = append(res.Packages, chosen[n])
	}
	return res
}

func pickWheel(cands []Wheel, spec string) (best *Wheel, sawSDist bool) {
	for i := range cands {
		w := &cands[i]
		if spec != "" && !matchSpec(w.Version, spec) {
			continue
		}
		if w.Kind == "sdist" {
			sawSDist = true
			continue
		}
		if best == nil || cmpVer(w.Version, best.Version) > 0 {
			best = w
		}
	}
	return best, sawSDist
}

func splitReq(req string) (name, spec string) {
	for i, r := range req {
		if r == '=' || r == '<' || r == '>' || r == '!' || r == '~' || r == ' ' {
			return strings.TrimSpace(req[:i]), strings.TrimSpace(req[i:])
		}
	}
	return req, ""
}

func matchSpec(version, spec string) bool {
	for _, part := range strings.Split(spec, ",") {
		part = strings.TrimSpace(part)
		if part == "" || part == "*" {
			continue
		}
		switch {
		case strings.HasPrefix(part, "=="):
			if version != strings.TrimPrefix(part, "==") {
				return false
			}
		case strings.HasPrefix(part, "!="):
			if version == strings.TrimPrefix(part, "!=") {
				return false
			}
		case strings.HasPrefix(part, ">="):
			if cmpVer(version, strings.TrimPrefix(part, ">=")) < 0 {
				return false
			}
		case strings.HasPrefix(part, "<="):
			if cmpVer(version, strings.TrimPrefix(part, "<=")) > 0 {
				return false
			}
		case strings.HasPrefix(part, ">"):
			if cmpVer(version, strings.TrimPrefix(part, ">")) <= 0 {
				return false
			}
		case strings.HasPrefix(part, "<"):
			if cmpVer(version, strings.TrimPrefix(part, "<")) >= 0 {
				return false
			}
		default:
			if version != part {
				return false
			}
		}
	}
	return true
}

func cmpVer(a, b string) int {
	as := splitVer(a)
	bs := splitVer(b)
	n := len(as)
	if len(bs) > n {
		n = len(bs)
	}
	for i := 0; i < n; i++ {
		ai, bi := 0, 0
		if i < len(as) {
			ai = as[i]
		}
		if i < len(bs) {
			bi = bs[i]
		}
		if ai != bi {
			return ai - bi
		}
	}
	return 0
}

func splitVer(v string) []int {
	v = strings.TrimPrefix(v, "v")
	if i := strings.IndexAny(v, "abrc"); i > 0 {
		// 丢掉本地/预发布后缀，比较只看数字段。
		head := v[:i]
		if _, err := strconv.Atoi(string(head[len(head)-1])); err == nil {
			v = head
		}
	}
	var out []int
	for _, p := range strings.Split(v, ".") {
		n := 0
		for _, r := range p {
			if r < '0' || r > '9' {
				break
			}
			n = n*10 + int(r-'0')
		}
		out = append(out, n)
	}
	return out
}

func sortStrings(s []string) {
	for i := 1; i < len(s); i++ {
		j := i
		for j > 0 && s[j] < s[j-1] {
			s[j], s[j-1] = s[j-1], s[j]
			j--
		}
	}
}