package staffing

import (
	"os"
	"strconv"
	"time"

	"github.com/shopspring/decimal"
)

// Config holds the W3 tunables. Every value is a GLOBAL platform default (see Load, which reads optional
// MM_W3_* environment variables). The staffing floor and the adjacency threshold may ADDITIONALLY be
// overridden per run through the request body, and the values actually used are recorded in
// recommendation_runs.parameters so a run is reproducible and auditable. Per org configuration is a future
// addition; v1 is global defaults plus per run override of the floor and the adjacency threshold.
type Config struct {
	// StaffingFloor is the minimum engine total a candidate must reach to be qualified for assignment.
	// Default 75, the Yellow band floor. A candidate below the floor is never an assign or reassign; the
	// optimizer and the classifier only ever arbitrate among candidates the engine already qualified.
	StaffingFloor decimal.Decimal
	// AdjacencyThreshold is the maximum cosine distance for a held skill to count as adjacent to a missing
	// required skill (the reskill path). Default 0.40 (roughly cosine similarity 0.60).
	AdjacencyThreshold decimal.Decimal

	// Confidence is a deterministic transparency aid in [0,1], a weighted blend of fit, clearance
	// provenance, and profile completeness. The three weights sum to 1.
	ConfidenceFitWeight          decimal.Decimal // default 0.60
	ConfidenceProvenanceWeight   decimal.Decimal // default 0.25
	ConfidenceCompletenessWeight decimal.Decimal // default 0.15

	// Value function. The optimizer objective is an int64 so the solve is integer exact and FIPS clean.
	ValueScalePrecision int64           // fixed integer scale applied to the real valued objective; default 1_000_000
	ValueReference      decimal.Decimal // the opportunity dollar value that maps to the midpoint priority; default 5_000_000
	PriorityMin         decimal.Decimal // minimum priority multiplier; default 1
	PriorityMax         decimal.Decimal // maximum priority multiplier; default 3

	// Optimizer envelope (denial of service guard on our own API): a portfolio solve that exceeds either
	// bound is refused with a typed error, never run unbounded.
	MaxProblemEdges int           // max candidate by requirement edges; default 250_000
	MaxProblemNodes int           // max graph nodes; default 5_000
	SolveBudget     time.Duration // per solve wall clock budget enforced by a context deadline; default 5s

	// ProactiveBestFitLimit caps the best fit opportunities returned per candidate in the proactive view.
	ProactiveBestFitLimit int // default 5
	// ReadPageMax caps a single page of recommendation reads.
	ReadPageMax int // default 200
}

// DefaultConfig returns the documented global defaults.
func DefaultConfig() Config {
	return Config{
		StaffingFloor:                decimal.NewFromInt(75),
		AdjacencyThreshold:           decimal.RequireFromString("0.40"),
		ConfidenceFitWeight:          decimal.RequireFromString("0.60"),
		ConfidenceProvenanceWeight:   decimal.RequireFromString("0.25"),
		ConfidenceCompletenessWeight: decimal.RequireFromString("0.15"),
		ValueScalePrecision:          1_000_000,
		ValueReference:               decimal.NewFromInt(5_000_000),
		PriorityMin:                  decimal.NewFromInt(1),
		PriorityMax:                  decimal.NewFromInt(3),
		MaxProblemEdges:              250_000,
		MaxProblemNodes:              5_000,
		SolveBudget:                  5 * time.Second,
		ProactiveBestFitLimit:        5,
		ReadPageMax:                  200,
	}
}

// Load returns DefaultConfig with any MM_W3_* overrides applied. Unset or unparseable variables keep the
// default, so a misconfigured env never silently disables a guard.
func Load() Config {
	c := DefaultConfig()
	if v := envDecimal("MM_W3_STAFFING_FLOOR"); v != nil {
		c.StaffingFloor = *v
	}
	if v := envDecimal("MM_W3_ADJACENCY_THRESHOLD"); v != nil {
		c.AdjacencyThreshold = *v
	}
	if v := envDecimal("MM_W3_VALUE_REFERENCE"); v != nil && v.GreaterThan(decimal.Zero) {
		c.ValueReference = *v
	}
	if n := envInt("MM_W3_MAX_PROBLEM_EDGES"); n > 0 {
		c.MaxProblemEdges = n
	}
	if n := envInt("MM_W3_MAX_PROBLEM_NODES"); n > 0 {
		c.MaxProblemNodes = n
	}
	if n := envInt("MM_W3_SOLVE_BUDGET_MS"); n > 0 {
		c.SolveBudget = time.Duration(n) * time.Millisecond
	}
	return c
}

// WithOverrides returns a copy of the config with a per run staffing floor and adjacency threshold
// applied when supplied (non nil). The caller validates the ranges before calling.
func (c Config) WithOverrides(floor, adjacency *decimal.Decimal) Config {
	if floor != nil {
		c.StaffingFloor = *floor
	}
	if adjacency != nil {
		c.AdjacencyThreshold = *adjacency
	}
	return c
}

func envDecimal(key string) *decimal.Decimal {
	s := os.Getenv(key)
	if s == "" {
		return nil
	}
	d, err := decimal.NewFromString(s)
	if err != nil {
		return nil
	}
	return &d
}

func envInt(key string) int {
	s := os.Getenv(key)
	if s == "" {
		return 0
	}
	n, err := strconv.Atoi(s)
	if err != nil {
		return 0
	}
	return n
}